A linear topology can only protect against single fiber link failures. Thus, a “1:1” linear system has an equal number of working and protection links; a “1:N” linear system has N working channels and one shared protection channel.
Lately, rings have become the topology of choice in fiber deployment. The prime motivator for rings versus linear transport is higher survivability. A ring protects against simultaneous failure of the protection and working fibers (i.e. cable cuts) and saves the intra-ring and inter-ring passthrough traffic during node failure/isolation. Rings offer cost effective transport solutions while delivering enhanced network survivability.
Currently, two types of rings are used, namely, unidirectional path switched rings (UPSR), and bidirectional line switched rings (BLSR). The UPSRs are currently used in access networks and therefore they are built for lower rates, which are sufficient for access link demands. UPSR protection switching is done at the SONET path level. The operation of UPSRs is standardized by the BellCore GR-1400-CORE standard, and there are OC-3/12 rate products available. The BLSR are currently used in the backbone networks and therefore they are built for higher rates. Switching is done at the SONET line layer. The operation of BLSRs is standardized by the BellCore GR-1230-CORE standard, and there are OC-12/48 rate products available.
The paper “Cycle-oriented Distributed Preconfiguration: Ring-like Speed with Mesh-like Capacity for Self-planning Network Restoration” by W. Grover et al, 1998 IEEE, pg. 537–543 describes a strategy of pre-failure cross-connection between the protection links of a mesh network, which achieves restoration of connections with little additional spare capacity. While the protection links are connected into p-Cycles, the method is different than self-healing rings because each pre-configured cycle contributes to the restoration of more failure scenarios than can a ring. If a span ‘on’ the p-Cycle fails, the cycle contributes with one restoration path. If a span off the cycle, but straddling it fails, two restoration paths may be obtained from a cycle.
The next step in evolution of communications is the agile photonic network APN, where the current point-to-point linear/ring architecture characterized by fixed channel allocation is replaced by an agile architecture characterized by a flexible end-to-end channel allocation. Agile photonic networks combine a few basic concepts to deliver cost reduction and scalability of the network, while enabling rapid set-up of bandwidth.
Transparency leverages all-optical switching to facilitate cost-effective connection set-up across multiple segments of the network, without having to undergo optical-electrical-optical conversions. Transparent photonic switching enables cost savings, space and power reduction, and also the ability to rapidly turn up new wavelengths across a network. Full range tunability provides the mechanism to deploy generic capacity pools, reducing over-provisioning and risk of stranded capital, and making transparency and agile reach manageable. In addition, operational viability of the APN requires that these concepts be automated and simplified. Such a network is described in the U.S. patent application “Architecture For A Photonic Transport Network”, (Roorda et al.), Ser. No. 09/876,391, filed Jun. 7, 2001 and assigned to Innovance Inc.
The APN allows activation of wavelengths from any point to any other point across the network. This function is automated to accommodate the addition or reconfiguration of wavelength patterns to manage changes of connection patterns and incremental network growth. The APN is able to automatically provision the routes in an efficient manner to allow revenue collection based on the class of service of each individual connection. The route provisioning mechanism is based on wavelengths becoming resources deployable and manageable across the network.
Since the operation of the agile network differs from that of pt—pt networks, traditional traffic protection schemes (electrical) are not directly applicable to optical switching. On the other hand, agility offers more flexibility in designing protections schemes based on various opportunities and perspectives.
There is a need to optimize wavelength utilization for the protection traffic in a mesh connected agile photonic network.